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CENTRAL NERVOUS SYSTEM
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Central nervous system (CNS)
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Functions of the spinal cord
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brain and spinal cord enclosed in bony coverings
spinal cord reflexes
integration (summation of inhibitory and excitatory) nerve
impulses
highway for upward and downward travel of sensory and
motor information
Brain functions
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sensations, memory, emotions, decision making, behavior
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INCOMING INFORMATION-RECEPTORS
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Respond to stimuli:
 nerve endings (dendrites of neurons)
 sense organs (taste)
Sensory Pathway (PNS)
Afferent neurons
somatic and visceral sensory neurons
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MOTOR PATHWAY (PNS)
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Efferent neurons
Stimulate and control effectors
 somatic motor neurons
 visceral motor neurons
Autonomic Nervous System (ANS)
• Sympathetic
• Parasympathetic
They both control the same effectors (with few
exceptions) but have opposite responses in
the effectors
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OVERVIEW OF SPINAL CORD
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Information highway between brain and body
Each pair of spinal nerves receives sensory information
and issues motor signals to muscles and glands
Spinal cord is a component of the CNS while the spinal
nerves are part of the PNS
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FUNCTIONS OF THE SPINAL CORD
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Conduction
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Locomotion
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bundles of fibers passing information up and down spinal
cord
repetitive, coordinated actions of several muscle groups
central pattern generators are pools of neurons providing
control of flexors and extensors (walking)
Reflexes
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involuntary, stereotyped responses to stimuli (remove hand
from hot stove)
involves brain, spinal cord and peripheral nerves
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ANATOMY OF THE SPINAL CORD
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Cylinder of nerve tissue within the vertebral canal (thick
as a finger)
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vertebral column grows faster so in an adult the spinal cord
only extends to L1
31 pairs of spinal nerves arise from cervical, thoracic,
lumbar and sacral regions of the cord
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each cord segment gives rise to a pair of spinal nerves
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MENINGES OF THE SPINAL CORD
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3 Fibrous layers enclosing spinal cord
Dura mater
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tough collagenous membrane surrounded by epidural
space filled with fat and blood vessels
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Arachnoid mater
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epidural anesthesia utilized during childbirth
layer of simple squamous epithelium lining dura mater and
loose mesh of fibers filled with CSF
(creates subarachnoid space)
Pia mater
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delicate membrane adherent to spinal cord
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MENINGES OF VERTEBRA AND SPINAL CORD
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CROSS-SECTIONAL ANATOMY OF THE SPINAL
CORD
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Central area of gray matter shaped like a butterfly and
surrounded by white matter in 3 columns
Gray matter = neuron cell bodies with little myelin
White matter = myelinated axons
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AREAS IN THE SPINAL CORD
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Pair of dorsal or posterior horns
 dorsal root of spinal nerve is totally sensory fibers
Pair of ventral or anterior horns
 ventral root of spinal nerve is totally motor fibers
Connected by gray commissure punctured by a central canal
continuous above with 4th ventricle
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WHITE MATTER IN THE SPINAL CORD
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White column = bundles of myelinated axons that carry signals up and down
to and from brainstem
3 pairs of columns or funiculi
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dorsal, lateral, and anterior columns
Each column is filled with named tracts (fibers with a similar origin,
destination and function)
Ascending and descending tract head up or down
Contralateral means origin and destination are on opposite sides while
ipsilateral means on same side
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REFLEXES
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Automatic response to change in environment
Integration center for spinal reflexes is gray matter of
spinal cord
Examples
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somatic reflexes result in skeletal muscle contraction
autonomic (visceral) reflexes involve smooth & cardiac muscle
and glands.
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heart rate, respiration, digestion, urination, etc
Reflexes can be:
 simple
 involve peripheral nerves and the spinal cord
 spinal reflexes
 learned (acquired)
 involve peripheral nerves and the brain
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REFLEX ARC
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Specific nerve impulse pathway
5 components of reflex arc
 Receptor
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Sensory neuron
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Transmits the response to the effector
Effector
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Part of the CNS that processes the information and generates
response
Motor neuron
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Transmits stimuli to the CNS
Integrating center
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Registers stimuli
Muscle or gland
4 important somatic spinal reflexes
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stretch, tendon, flexor(withdrawal) & crossed extensor reflexes
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THE PATELLAR TENDON REFLEX ARC
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CENTRAL NERVOUS SYSTEM-THE BRAIN
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THE BRAIN
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Longitudinal fissure - cerebral hemispheres.
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gyri = folds; sulci = grooves
cortex = surface layer of gray matter
nuclei = deeper masses of gray matter
tracts = bundles of axons (white matter)
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MEDIAN SECTION OF THE BRAIN
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GRAY AND WHITE MATTER
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Gray matter = neuron cell bodies, dendrites,
and synapses
 forms
cortex over cerebrum and cerebellum
 forms nuclei deep within brain
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White matter = bundles of axons
 forms
tracts that connect parts of brain
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MENINGES OF THE BRAIN
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VENTRICLES AND CEREBROSPINAL FLUID
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Internal chambers within the CNS
 lateral
ventricles in cerebral hemispheres
 third ventricle = single vertical space under
corpus callosum
 cerebral aqueduct runs through midbrain
 fourth ventricle = chamber between pons and
cerebellum
 central canal runs down through spinal cord
Lined with ependymal cells
 Choroid plexus produce CSF
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BRAIN VENTRICLES
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CEREBROSPINAL FLUID
Fills ventricles and subarachnoid space
 Brain produces and absorbs 500 ml/day
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 choroid
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plexus creates by filtration of blood
Functions
 floats
brain so it is neutrally buoyant
 cushions from hitting inside of skull
 chemical stability -- rinses away wastes
Escapes (4th ventricle) to surround brain
 Absorbed into venous sinus by arachnoid villi
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HINDBRAIN - MEDULLA OBLONGATA
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Cardiac center
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Vasomotor center
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control rate and depth of breathing
Reflex centers
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adjusts blood vessel diameter
Respiratory centers
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adjusts rate and force of heart
for coughing, sneezing, gagging, swallowing,
vomiting, salivation, sweating, movements of
tongue and head
Most of the fibers are crossing over
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Left cortex controls right side of body
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PONS
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Bulge in brainstem, superior to
medulla
Ascending sensory tracts
Descending motor tracts
Pathways in and out of cerebellum
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Nuclei
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concerned with posture, sleep, hearing,
balance, taste, eye movements, facial
expression, facial sensation, respiration,
swallowing, and bladder control
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CEREBELLUM
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Two hemispheres connected by
vermis
Cortex = surface folds called
folia
Output comes from deep gray
nuclei
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granule and purkinje cells
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CEREBELLUM
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White matter (arbor vitae)
visible in sagittal section
Evaluation of sensory
input
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coordination and locomotor
ability
spatial perception
Timekeeping center
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predicting movement of objects
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MIDBRAIN - CROSS SECTION
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Tegmentum
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Substantia nigra
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connects to cerebellum
and helps
control fine movements
through red nucleus
sends inhibitory signals to
basal ganglia and
thalamus (degeneration
leads to tremors and
Parkinson disease)
Central gray matter =
pain awareness
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RETICULAR ACTIVATING SYSTEM
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Scattered nuclei in medulla, pons &
midbrain
Reticular activating system
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alerts cerebral cortex to sensory signals
(sound of alarm, flash light, smoke or
intruder) to awaken from sleep
maintains consciousness & helps keep you
awake with stimuli from ears, eyes, skin and
muscles
Motor function is involvement with
maintaining muscle tone
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DIENCEPHALON: THALAMUS AND
HYPOTHALAMUS
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Thalamus Functions
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Relays signals from cerebellum to
motor cortex
Emotional and memory functions
Hypothalamus Functions
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hormone secretion
autonomic NS control
thermoregulation
food and water intake (hunger and
satiety)
sleep and circadian rhythms
memory (mammillary bodies)
emotional behavior
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CEREBRUM -- GROSS ANATOMY
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Cerebral cortex - 3mm layer of gray matter
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extensive folds increase surface area - divided into lobes
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FUNCTIONS OF CEREBRUM - LOBES
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Frontal
 voluntary
motor functions
 planning, mood, smell and social judgement
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Parietal
 receives
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Occipital
 visual
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and integrates sensory information
center of brain
Temporal
 areas
for hearing, smell, learning, memory, emotional
behavior
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TRACTS OF CEREBRAL WHITE MATTER
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Most of cerebrum is white
matter
Types of tracts
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projection tracts
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from brain to spinal cord, forms
internal capsule
commissural tracts
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cross to opposite hemisphere
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corpus callosum
anterior and posterior commissures
association tracts
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connect lobes and gyri within a
hemisphere
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LIMBIC SYSTEM
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Loop of cortical structures
 amygdala,
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hippocampus and cingulate gyrus
Role in emotion and memory
 pleasure
and aversion centers
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MEMORY
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Information management
 requires
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learning, memory and forgetting
Amnesia
 anterograde
amnesia - no new memories
 retrograde amnesia – can’t remember old ones
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Hippocampus
 organizes
sensory and cognitive information into a
new memory
Cerebellum – helps learn motor skills
 Amygdala - emotional memory
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AUTONOMIC NERVOUS SYSTEM
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Visceral motor neurons control
 heart rate
 breathing rate
 digestion
 blood pressure
 salivation
Nerve impulses of these motor neurons start in the CNS
(medulla oblongata and pons)
 Pathway through:
Spinal cord
 Cranial nerves
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SYMPATHETIC DIVISION
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The sympathetic division is called the “fight or flight”
system
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when the body needs to generate energy
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exercise, excitement, emergency, and embarrassment
Fight or flight response
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increases heart rate, blood pressure, respiration rate, blood
flow to skeletal muscles, glucose metabolism
decreases the activities that are not essential at the
moment (digestive system organs are subdued- decreased
blood flow to that system
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PARASYMPATHETIC DIVISION
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The parasympathetic division is called the “rest and
digest”
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activated when the body needs to conserve energy
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digestion, defecation, and diuresis (urination)
Promotes necessary changes during these activities
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decreases heart rate, blood pressure, respiration rate,
blood flow to skeletal muscles, glucose metabolism
increases the activity of and blood flow to the digestive
system organs
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ORGANIZATION OF THE SYMPATHETIC DIVISION
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EFFERENT SYMPATHETIC VS. PARASYMPATHETIC
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EFFECTS OF NEUROTRANSMITTERS OF THE AUTONOMIC
NERVOUS SYSTEM
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The cells of each organ controlled by the ANS have both ACh and
NE receptors
 organs are dually controlled
The response of the organ is determined by the identity of the
neurotransmitter released
 the binding of ACh to its receptor will cause the effector to
respond in one way
 the binding of NE to its receptor will cause the effector to
respond in the opposite way
The effect of ACh and NE is effector specific
 NE increases heart rate, ACh decreases heart rate
 NE decreases the secretion of saliva, ACh increases the
secretion of saliva
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